The present invention generally relates to heating, ventilating, and air-conditioning, (HVAC), and more particularly to use of a common filtration unit for building makeup air and emergency exhaust.
Nuclear, biological, and chemical (NBC) attacks are an increasing threat in the modern world. Occupants of a building can be protected from the release of NBC agents outside or inside the building by filtering the air with NBC filtration units. An NBC filtration unit typically only allows one particle greater than one micrometer in a million to pass through the filtration unit. This requires very high construction standards. In addition, a powerful blower is required to maintain airflow due to a pressure drop through the filtration unit. These filtration units with blowers can cost between $100,000 and $250,000 or more for a typical 16,000 cubic feet per minute (CFM) unit.
Typically, the best defense against an outside release of an NBC agent is to filter the contaminated air before it enters the building through a makeup air unit. For internal releases, the most effective general protection strategy is to exhaust the building from the vicinity of the release of the NBC agent. The exhausted contaminated air is filtered before it is released outside to prevent contamination of neighboring buildings. Typically, the intake air filtration system and the emergency exhaust filtration system require two separate NBC filtration units. Installing and maintaining two NBC filtration units in a building is expensive.